1. Field of the Invention
The present invention relates to gun barrel rifling and, more particularly, to rifling having a varying radial spacing between the surface of the lands and the bottom surfaces of the interleaved grooves as a function of distance along the barrel.
2. Description of Related Art
A conventional gun barrel of a firearm includes a bore having rifling formed therein. That is, the rifling usually includes a plurality of helical, sometimes referred to as spiral, radially inwardly facing lands with interleaved grooves. The surfaces of these lands are usually arcuate corresponding in curvature with the respective radius from the axis of the bore. Other configurations of the surfaces of the lands are known. Each of the grooves usually includes a bottom surface also arcuate as a function of the radius from the axis of the bore. Other configurations for the bottom surfaces of the grooves are known. Generally, the sides interconnecting the lands with the bottom surfaces of the grooves are essentially radially aligned. However, other surface configurations interconnecting the lands with the bottom surfaces of the grooves are known.
Typically, six lands and corresponding six grooves are equiangularly displaced about the bore of the barrel. For purposes of terminology, the term land diameter means the distance from one land to a radially opposing land. The groove diameter is the distance from the bottom surface of one groove to the bottom surface of a radially opposing groove. The diameter (caliber) of the projectile or bullet fired through a barrel usually corresponds with the groove diameter. To define the distance between the surface of a land and the longitudinal axis of the bore and the distance between the bottom surface of a groove and the longitudinal axis of the bore, the terms land radius and groove radius, respectively, may be used.
As a firearm is discharged, the gases generated within the casing propel or fire the bullet through the barrel. Because the land diameter is less than the diameter of the usually cylindrical part of the bullet, the lands will engrave corresponding channels in the bullet. As the bullet travels toward the muzzle, the channels interacting with the respective lands, will cause the bullet to rotate about its longitudinal axis at a rate commensurate with the helix (or spiral) of the lands and the velocity/acceleration of the bullet traveling through the bore of the barrel.
Upon close inspection of bullets fired through a barrel, it has been learned that the grooves formed in the bullet by the respective lands are often not of the same uniform depth. Such lack of uniformity of depth suggests that the longitudinal axis of the bullet is not coincident with the longitudinal axis of the bore of the barrel. Without such coincidence, the bullet will be laterally displaced as it is longitudinally displaced during its travel through the bore. Assuming that the center of gravity of the bullet is located on its longitudinal axis, the asymmetric depth of the grooves in the bullet will cause the center of gravity of the bullet to move in a helix (spiral) as the bullet translates through the bore. Upon discharge of the bullet from the muzzle, the spinning motion of the bullet will have a lateral velocity component of some degree. Such lateral velocity component will result in inaccuracy of travel as a function of the degree of lateral velocity component present. As it is unlikely that any two consecutively fired bullets will have exactly the same degree of lateral velocity component, different paths or trajectories will be followed by each bullet. Such different trajectories will result in non-correspondence of the bullets striking the same point on a target, assuming all other variables of windage, etc. being constant.
As a projectile or bullet begins to travel down the bore of a gun barrel upon discharge of a firearm, a plurality of the lands tapering radially inwardly engrave or form channels in the bullet to guide the bullet and cause it to spin as a function of the helix (or spiral) of the rifling. The pressure of the gases behind the bullet in combination with the resistance to forward travel of the bullet induced by the lands of the rifling, as well as the inertia of the bullet, causes the material of the bullet to expand radially to a greater or lesser degree into the grooves interleaving the lands. Toward the muzzle of the barrel, the ratio of the land diameter to the groove diameter is increased to induce the material of the bullet to come into uniform contact with the bottom surface of each of the grooves to centralize the bullet within the bore and to ensure that the spin of the bullet is essentially about its longitudinal axis and hence about the center of gravity of the bullet to minimize or eliminate any lateral velocity component of the bullet. To increase the ratio of the land diameter to the groove diameter, the lands may taper radially outwardly toward the bore surface, and hence toward the bottom surface of the grooves, or the bore may be reduced to bring the groove diameter toward the land diameter.
It is therefore a primary object of the present invention to reduce any lateral velocity component of a projectile as it translates through the rifling in a barrel of a firearm.
Another object of the present invention is to induce the material of a projectile traveling through a rifled bore to become supported by the bottom surfaces of the grooves interleaving the lands in the bore.
Still another object of the present invention is to increase the ratio of the land diameter to the groove diameter toward the muzzle of a rifled barrel of a firearm.
A further object of the present invention is to provide varying depth grooves in a rifled barrel of a firearm to urge a projectile discharged from the barrel to spin about its longitudinal axis and without any lateral velocity component.
A still further object of the present invention is to provide a rifled barrel of a firearm having an increased land diameter in proximity to the muzzle.
A yet further object of the present invention is to provide a rifled barrel of a firearm having a reduced groove diameter in proximity to the muzzle.
A yet further object of the present invention is to provide a method for reducing the lateral velocity component of a projectile traveling through the barrel rifling of a firearm.
These and other objects of the present invention will become apparent to the those skilled in the art as a description thereof proceeds.